Dunn sustained "a lot of trauma" to an arm and particularly his hand, as well as other injuries, which were not considered life-threatening, Johnson said.
Part of Dunn's hand, including several fingers, were severed by the crash, said UHP Lt. Steve Winward.
The trooper's hand may have been caught between the door of his UHP squad car and the vehicle's body at the time of the accident, said UPD Lt. Justin Hoyal.
UPD investigators say the 21-year-old man driving a Mitsubishi flatbed truck reported having experienced difficulty shifting gears shortly before the accident. The UHP unit was one of several parked in an outside lane processing the initial crash; the truck was eastbound in the next lane over.
"The driver said he looked down briefly at the gear shift and drifted into the outside lane, hitting the [UHP] unit," Hoyal said. "Dunn apparently had the door open and was in the process of getting back into his unit" when the crash occurred.
The driver of the truck, though shaken, did not suffer physical injuries, Hoyal said.
No citations were immediately issued. Hoyal said once UPD investigators conclude their reconstruction of the accident, they will submit their findings to the Salt Lake County District Attorney's Office for screening of charges.
Winward said Dunn was anticipated to be out of surgery, following operations that were anticiapted to take several hours, by 6:30 p.m.
Troopers had been at the hospital throughout the day and they had been checking in with Dunn's wife, who dispatches for UHP, to make sure she and her family were alright, Winward added.
The accident involving the trooper occurred at 8:26 a.m. near Lambs Canyon. The trooper was there investigating an earlier 6:27 a.m. crash in which a van rear-ended a semi-trailer truck.
The driver of the van was flown to University Hospital in critical condition but with injuries that were not considered life-threatening.
Several other, more minor and non-injury accidents were reported in the same general area as a result of traffic constriction due to the van-semi crash.
Winward noted that Dunn is the fifth trooper to be struck by a vehicle this year and he urged drivers need to watch out for them.
"If they see the red and blues, pay attention, slow down and allow the troopers plenty of space," he said.